1. Field of the Invention
The present invention relates to the testing of semiconductor devices. More particularly, the present invention relates to a loader which is used in a burn-in test.
2. Description of the Related Art
A burn-in test is a reliability test which is performed before electronic components, such as memories or logic devices, are graded acceptable. In particular, the burn-in test applies severe stress in the form of a high temperature, a voltage, a pulse (clock) or the like, to semiconductor devices to in effect speed up a point in time at which a defective semiconductor device fails. Thus, the defective semiconductor devices are detected early on, and only the good semiconductor devices are subjected to a final electrical test and are then sent out.
The burn-in test includes the steps of: a) loading a semiconductor package onto a burn-in board having a test socket, b) testing the semiconductor package loaded on the burn-in board for a certain period of time while a stress produced by a burn-in system is applied to the semiconductor package, and c) unloading a burn-in tested semiconductor package from the burn-in board. In this test, a loader is used to load the semiconductor package onto and unload the semiconductor package from the test socket of the burn-in board.
FIG. 1 is a schematic front view of a general loader of semiconductor package testing device. Referring to FIG. 1, the loader 1 generally includes a main loader body 10, a main nozzle body 20 capable of vertical movement, a vacuum suction head 30, and a socket cover depressing head 40. The vacuum suction head 30 is connected to the bottom of the main nozzle body 20, and picks up a semiconductor package 50 using suction. The socket cover depressing head 40 extends around the main nozzle body 20 and the vacuum suction head 30, and depresses the socket cover of a test socket.
When the semiconductor package 50 is to be lifted and unloaded from the test socket, the main nozzle body 20 descends and picks up the semiconductor package 50 using the vacuum suction head 30. On the other hand, when the semiconductor is to be loaded onto the test socket, the suction from the vacuum suction head 30 is turned off while the main nozzle body 20 remains still, thereby dropping the semiconductor package 50 onto the test socket 50.
FIG. 2 is a schematic front view of the test socket which is used with the loader shown in FIG. 1. Referring to FIG. 2, the test socket includes a main body 60, a socket cover 62, a support bar 64, an adapter 66 and wiring 72. The support bar 64 acts as a spring which contracts/retracts when the socket cover 62 is depressed. Once the socket cover 62 is depressed, the adapter 66 guides a semiconductor package, that is dropped by the loader 1, to a position where an electrical connection between the package and the wiring 72 is established.
FIG. 3 is a plan view of the test socket and FIG. 4 shows the test socket with the socket cover 62 depressed. Referring to FIGS. 3 and 4, the wiring 72 extends to a flat connection plate 68 in which connection contacts 70 are located. The adapter 66 is disposed inside the socket cover 62, and the flat connection plate 68 is, in turn, located within the adapter 66. Thus, when a semiconductor package is loaded onto the flat connection plate 68, external connection terminals of the semiconductor package, for example, solder balls, are connected to the connection contacts 70 within the flat connection plate 68. The semiconductor package is subjected to the burn-in test in this state.
The size of the adaptor 66 varies according to the size of the semiconductor package which is to undergo the burn-in test. On the other hand, the flat connection plate 68 can accommodate semiconductor packages of all sizes. However, without the adaptor 66 present, the solder balls of the semiconductor package might not be aligned with, i.e., electrically connected to, the connection contacts 70 when dropped onto the test socket by the loader 1.
Referring now to FIG. 4, in particular, even if a semiconductor package is dropped from a loader while the solder balls of the package are not disposed directly over the corresponding connection contacts 70, the inclined walls A of the adaptor 66 align the semiconductor package with the connection contacts. That is, the solder balls of the semiconductor package are correctly seated on the connection flat plate 68 and are thus electrically connected to the connection contacts 70.
FIG. 5 is a flowchart illustrating a method of using a conventional loader for semiconductor package testing. Referring to FIG. 5, the main nozzle body 20 of the loader 1 is lowered whereupon the vacuum suction head 30 of the loader 1 picks up a semiconductor package from the top using suction. Then, the loader 1 is moved over a test socket. Thereafter, the socket cover depressing head 40 of the loader 1 depresses the socket cover 62 of the test socket. Then, the suction of the vacuum suction head 30 of the loader 1 is turned off, whereby the semiconductor package is dropped onto the test socket. The falling semiconductor package is aligned by the adaptor 66 of the test socket, so that solder balls of the semiconductor package, which constitute external connection terminals of the semiconductor package, are connected to the connection contacts 70 of the test socket. In this state, the semiconductor package is tested under the internal electrical control of the loader equipment.
The use of the above-described loader for semiconductor package testing has the following problems. The test socket can be used only for semiconductor packages of the same size because of the adaptor. For example, a 1.2 cmxc3x971.2 cm semiconductor package can not be tested using a burn-in test socket having an adaptor configured for a 1 cmxc3x971 cm semiconductor package.
Therefore, a large number of burn-in boards are required for burn-in testing. The fabrication and management of this large number of burn-in boards is costly, and requires a lot of manpower and production storage space.
Accordingly, one object of the present invention is to provide a loader, for use in semiconductor package testing equipment, having a package guider which allows one test socket to be used for testing semiconductor packages of different sizes.
To achieve the first object, the present invention provides a loader including a main loader body, a main nozzle main body having a vacuum line therein and capable of moving vertically below the main loader body, a vacuum suction head integrated with the bottom of the main nozzle body, a socket cover depressing head extending around the main nozzle body and the vacuum suction head, below the main loader body, for depressing the socket cover of a test socket, and a package guider for guiding a semiconductor package as it falls from the vacuum suction head.
The test socket will be similar to that of a conventional burn-in test socket but in this case has no adaptor. The semiconductor packages to which the present invention is particularly well-suited are ball grid array (BGA) packages and chip scale packages (CSP).
The package guider comprises an upper package guide member, a plurality of (preferably four) lower package guide members, connection springs connecting the lower guide members to the upper guide member, and a mechanism, such as a camming mechanism, for moving guide surfaces of the lower guide members toward and away from each other. Preferably, the lower package guide members are pushed outward by the operation of the camming mechanism when the main nozzle body descends, and are pursed together by the connection springs to form a space through which the semiconductor package must pass when the main nozzle body is raised to a loading position. The camming mechanism can be constituted by protrusions on the lower guide members which coact with the main nozzle body as it is raised and lowered, under a biasing force exerted thereon by the connection springs .
Also, the lower package guide members are preferably formed of a conductive material, such as steel, to prevent static charges from accumulating on the semiconductor package as the package slides along and is guided by the lower guide members.
Another object of the present invention is to provide a method of loading a semiconductor package onto a universal test socket, wherein the semiconductor package is aligned with the test socket regardless of the size of the package.
To achieve this object, the present invention provides a method in which, first, a semiconductor package is picked up using a vacuum suction head. The semiconductor package is then moved over a universal test socket, i.e. a test socket that has no adaptor. The semiconductor package is dropped onto the test socket by turning off the vacuum suction of the vacuum suction head of the loader. However, as the semiconductor package is being placed over the test socket, guide surfaces are moved inwardly toward one another into guiding positions at which the guide surfaces are located between the semiconductor package and the test socket. In this state, the guide surfaces delimit a space through which the semiconductor package must pass when dropped onto the test socket. Thus, any semiconductor package that is gripped by the vacuum suction head but is portioned thereby out of alignment with the test socket, will be guided by the guide surfaces into alignment with the test socket when the suction is cut off and the mis-aligned semiconductor package is dropped onto the test socket.
Also, when the package is positioned over the test socket, the distance between the bottom of the guide surfaces and the surface of the test socket onto which the package is to rest is set to be smaller than the thickness of the semiconductor package. In this way, the guide surfaces guide the package from the time the package is released from the vacuum suction head to the time the package comes to rest on the test socket.
According to the present invention, as summarized above, the same test socket can be used for semiconductor packages of all sizes. Therefore, the manufacturing and equipment management costs associated with the testing of the semiconductor packages can be reduced.